1. Field of the Invention
The present invention relates to a semiconductor device, and specifically to a semiconductor device on which a resistance is mounted to even out the current distribution to semiconductor elements of the semiconductor device.
2. Background Art
In a semiconductor device used in the inverter/converter of electric railways or the like, a rated current of several-hundred to several-thousand amperes is required. Therefore, several to several-ten semiconductor elements are normally connected in parallel in a semiconductor device.
For example, in Japanese Unexamined Patent Publication No. 2001-185679, the above-described semiconductor device, which has a plurality of semiconductor elements formed on an insulating substrate, is disclosed. On the insulating substrate, a resistance known as a gate balance resistance is disposed in the vicinity of each semiconductor element. The resistance is to even out the current distribution to each semiconductor device, and is fixed on the insulating substrate by soldering similarly to the semiconductor element. Furthermore, the insulating substrate is fixed on the heat sink by soldering.
When the above-described semiconductor element is in operation, a heat cycle occurs. Consequently, in the soldered portion, thermal stress caused by difference of coefficients of linear thermal expansion of each constituting member is generated, and the solder is gradually cracked. When the portion where the gate balance resistance is soldered is cracked, there has been a problem wherein the resistance value is elevated, and finally open-circuit defect is caused to generate withstand voltage defect.